Preparation of zinc propionate



Patented Oct. 19, 1948 UNITED STATES PAT OFFICE 1. 311 0 I PREBARATIQN 9F ZINC PROPIONATE Arthur George Weber, Wilmington, and Clement H. Hamblet, Gordon Heights, DeL, assignors to E. L dn Pont'de' Nemours & Company, Wilmington, 1161., a corporation of Delaware Nit-Drawing: Application. November 30, 1945, Serial No. 632,082;

fThisinvention relates to a process for the preparation of zinc salts of organic acids and more particularly to the preparation of zinc propiona-te. I GV'ari-ous methods have been proposed for the preparation of the zinc salts of the organic acids such, for example, as the reaction of the organic acid with a heavy'metal carbonate or by the exposure of the metal to the warm vapors of the organic acids, the latter procedure being em,- ployed for'the preparation of white lead,.requiring many days and in some cases Weeks in processing These slow and tedious processes are unsuitable for rapid economical formation of the zinc salts of organic acids. I d

An object of the present invention is to provide a process for the preparation of zinc salts of organic acids. Another object ofv the invention is to provide a process wherein organic acids can be converted to the corresponding zinc salt by direct contact with the metal. A further ob- 'J"e'ct of the invention is to provide a process wherein propionic acid is converted to its zinc salt by direct reaction of the acid with zinc in the presence of oxygen. Other objects and ad'- vantages of the invention will hereinafter appear. The above objects are accomplished in accord withthe broadest aspects of the invention by a process wherein an organic acid such as propionic acid is heated with zinc while in contact with oxygen. More specifically, the process m'ay be conducted bypassing an oxygenrcontaining gas such as air and the organic acid intoa converter charged with metal pellets, gas and acid flowing cocurrent or countercurrent through the con- "to verter. By this process it has "been found possible notonIy" to increase the reaction rate of" the heated at least to that temperature at which they are fluid in order that the oxygen or oxygencontaining gas can be easily bubbled through them. Generally speaking, however, temperatures may range between 50 and 200 C. and more-specifically for the fatty acids, temperal Claims'. (01.260-429') tures rangingbet-ween '70 and C. with a 'droxyjaci'dssuch, for example, as glycolic acid, lactic-acid, and tartaric acid; as well as polyc'arboxylic acids such, for example, as oxalic acid, glutaric acid and adipic acid; and the unsaturated acids such, for example, as acrylic acid, and methacrylic acid, as well as the aromatic acids such, for example, as benzoic acid.

1 Theprocess-may be carried out by a continuous or discontinuous procedure.

verter, of relatively great length to width, disposed in a vertical position and charged with zinc which maybe in the form of moss, chips, flakes, or metal pellets of a suitable diameter such as, for; example, from to /2 inch. If a water soluble organic acid higher than acetic is "to be convertedto the zinc salt it is introduced in an aqueous solution into the converter together "with an oxygen containing gas such as air and the reaction within the converter maintained at the optimum temperature for the particular type of acid being converted. When carried out in this, the preferred manner, the acid or acidand. water may be introduced at the top of the converter and the product collected from the bottom whil'e'air isperini'tted to bubble up through the descending acid and the process thereby con du cted under 'countercurrent flow conditions, the spent air being allowed to issue from the top of the converter carrying with it the water formed during the reaction, Contrariwise, both, acid and air can be introduced into the bottom of the converter to-give cocurrent flow, the product as well as the'spen-t air and water formed issuing from the toner the converter. To enhance the new of fluids within the converter, which increases the speed of the reaction, a portion of the reactants may be pumped from the top of the converter and reintroduced into the bottom'thereoi, the velocity and turbulence of the flow within the converter being regulated inpart by the amount and degreeoithis, recycled material. As will be appreciated by those skilled in the art, the red W H The former may, {for exampla-be illustrated by the use of a conwise which may be effected by charging a con-.

are to be made. When the zinc salt is soluble in the acid of which it made the temperature of the reaction is maintained above the transition point of the mixture, if a batchwise or continuous process is to be conducted. In some cases, the solution of acid and salt can be withdrawn from the converter, cooled down to precipitate the salt, the salt separated by filtration and the acid returned to the converter. Analogous to the latter type of procedure is that used for the prepartion of salts which are relatively verter such as that described above or any suit- .able vessel with the metal particles and the-acid to be reacted; the acid is raised to reaction temperature and the reaction continued until all of insoluble in the acid such as zinc propionate. Under such circumstances it is usually desirable to effect the reaction in a mutual solvent for the acid and salt (in the case of zinc propionate this solvent is water) from which the salt can be crystallized or otherwise separted after withthe acid has been converted to the salt where upon it Throughout the reaction air or oxygen or an oxygen-containing gas is bubbled through or otherwise dispersed into the liquid. During ;batchwise processing it is likewise desirable to recirculate the reactants which may be accomplished by an outside circuit provided with a suitable pump whereby the reactantsare removed and returned to the vessel in order to maintain a constant, preferably turbulent, flow within the .-vessel.; d

When aconverter of greater length than width is employed, anon-homogeneous liquid mixture is sometimes formed in the converter. Relatively water-insoluble acids or their salts which are relatively water-insoluble are responsible for this lack of homogeneity. Since the acid is generally lighter than the water, the latter tends to collect in the bottom of the converter during the initial stages of the reaction. As the reaction proceeds and the zinc salt increases in concentration in the converter the positions of water and acid andproduct in the converter are reversed. Unfortunately, this reversal in positiontakes place rapidly with a vaporization of an appreciable part of the water with the result that unless due precautions are taken a large part of the charge -will be blown from the top of the converter.

It has been found that the above disadvantageousresult can be eliminated by recycling some of the material fromthe converter through an external separator. This method inhibits the settling of large amounts of water during the initial stages of the reaction and thereby renders .it possible to conduct the reaction without loss of productsfrom this cause. t ,Thereaction of an organic acidv with zinc is exothermic and consequently after the reaction has been initiated no further heat input is requiredbut on the contrary it is usually desirable to provide means for withdrawing the heat of reaction in order to maintain the temperature within proper bounds. Some of the heat of the reaction is absorbed by the water discharged with the spent gas from the converter, another portion by the sensible heat in the spent gases but it foas been ifoundsthat in addition to these heat controlling means, it is oftendesirableto introduce water into the converter and utilize its sensible and latent heat to; control the reaction within the preferred temperature range.

As has been indicated the process is applicable to the conversion of any organic acid to its zinc .salt. Inasmuch as some zinc salts are soluble in a liquid consisting of the acid portion of the salt/ while others are not,,a different procedure jsrecommended when zinc salts of different types is discharged from the converter;

drawing it from the reaction converter, the unreacted acid being returned to the reaction.

The use of a, slovent may be illustrated by the preparation of zinc propionate wherein an aqueous solution containing propionic acid or less together with air is passed through a converter containing zinc; the product issuing from the converter is passed into a cooling and crystallizing chamber, the crystals of zinc propionate separted and the aqueous solution of propionic acid returned to the converter with make-up acid preferably after removal of water of reaction. The examples illustrate embodiments of the invention in which parts are by weight and to which the invention is not to be limited.

Example 1.A column having a height to diameter ratio of 40.1 was charged with 429.6 parts of mossy zinc and 316.0 parts of propionic acid. Air was passed upward through this mixture for a period of minutes at a space velocity of 34.5, the reaction mixture being maintained at 143- -l45 C. by external temperature controls. The product obtained was crystallized at 0 C. and filtered, giving a crystalline crop which after drying was found to contain 31.2% zinc (theory for zinc propionate-30.9% zinc). Example 2.A column having a height to diameter ratio of 28.1 was similarly charged with 395.0 parts of mossy zinc and 178.0 parts of a 75% solution of propionic acid in water. Nitrogen was passed upward through this mixture for a period of 70 minutes at a space velocity of 9, the reacting mixture being maintained at 129-130 C.

The small amount of zinc propionate recovered from the product corresponded to a production rate of only 3.5#/cu. ft./hr.

Example '3.When a charge similar to that described in Example 2 was treated in a column similar to that described in Example 2 at 129-130 C. with oxygen at a space volocity of 11,

,a copious yield ofzinc propionate was obtained in 55 minutes, average production rate corresponding to 11.3#/cu. ft./hr.

As shown by the examples, the rate of oxygen flow may be varied andit has been found that this variation may range between a space velocity of 1 and 10.0, space velocity beingdefined as the unit volume of air passing per hour per superficial volume occupied by the metal particles in the tower, the fluid volumes being determined under standard temperature and pressure conditions. While the examples have described the use of air and oxygen, inert gas-oxygen mixtures may be employed.

The use of an antioxidant is highly advantageous when unsaturated organic acids are converted to their zinc salts. The evolution of carbon dioxid indicates degradation of the acid or salt during the reaction and it has been found that the presence of an antioxidant inhibits and usually entirely eliminates this degradation. Suitable examples of antioxidants which may be employed are, in addition to the hydroquinone described in the examples, pyrogallol, phenol, phenyl-alpha-naphthyl amine, mesitols, and other suitable antioxidants. The antioxidant may be used in amounts ranging between 0.005 and 2% of the organic acid by weight with a preferred range particularly for hydroquinone between 0.01 and 0.02.

We claim:

1. A continuous process for the preparation of zinc propionate by reacting propionic acid'with metallic zinc which comprises reacting metallic zinc with an aqueous solution of propionic acid at a temperature between 50 and 200 C. while continuously during the reaction passing air through the reacting mixture the reaction being conducted by passing the reactants continuously into and the products continuously out of the reaction zone.

2. The process of claim 1 conducted with an air space velocity between 1 and 100.

3. The process of claim 1 conducted at a temperature between 70 and 150 C. and with an air space velocity between 1 and 100.

4. A process for the preparation of zinc pr'opionate from propionic acid and metallic Zinc which comprises passing at a temperature be- Q tween and 150 C. a aqueous solution of propionic acid over mossy zinc while bubbling air through the solution throughout the reaction, the reaction being conducted by passing the reactants continuously into and the products continuously out of the reaction zone.

ARTHUR GEORGE WBER.

CLEMENT H. HAMBLET.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Chemiker Zeitung, vol. 35, pages 242 and 243, Mailke.

Certificate of Correction Patent No. 2,452,003. October 19, 1948.

ARTHUR GEORGE WEBER ET AL.

It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows:

Column 4, line 34, Example 1, for 40.1 read 40:1 line 45, Example 2, for 28.1 read 28 :1; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 25th day of January, A. D. 1949.

THOMAS F. MURPHY,

Am'atant Commissioner of Patents. 

